Scielo RSS <![CDATA[Water SA]]> vol. 35 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>On the determination of trends in rainfall</b>]]> The question of how to assess trends in rainfall data is very relevant to that of climate change. A short review of prior work revealed that there was little consensus on the methodology to be adopted. Many methods had been tried and abandoned. Some methods had found comparatively wide acceptance although they employed a statistical software package that is not readily available, and which does not have tools common to other more widely available packages. In the light of this review, it was decided to start from the inherent distribution of rainfall and develop a method for determining temporal trends based on the underlying distribution. Data sets from 4 different locations and covering sample periods from every 5 min to every week were assessed. In each case it was found that the data could be represented extremely well by a log-normal distribution, which meant that normal statistics could be applied to the transformed data. When it was so applied, clear trends emerged, the significance of which could be readily judged via an F-test or t-test. Some worked examples are provided. Attention is drawn to the possibility of estimating the likelihood of extreme events by this method. It is also noted that the usual method of reporting rainfall as an arithmetic average overstates the precipitation, and that on statistical grounds use of a geometric mean is to be preferred. <![CDATA[<b>Oestrogenic activity in drinking waters from a rural area in the Waterberg District, Limpopo Province, South Africa</b>]]> In South Africa, limited data are available regarding possible oestrogenic activity in the aquatic systems and especially drinking water. Water in the rural areas is often contaminated with a complex mixture of toxic compounds originating from nearby industries, agriculture and households. In these rural areas the only access to drinking water is boreholes, natural springs and rivers. Thus human exposure to environmental contaminants in drinking water is potentially high. Two rural communities near Mokopane in the Waterberg district of the Limpopo Province were selected in order to screen for oestrogenic activity in drinking water sources in a rural area. Eleven 1 ℓ water samples (Molekane n= 4; Sekuruwe n= 7), were collected in prepared glass bottles and extracted on a SPE C18 cartridge and reconstituted into ethanol. The recombinant yeast oestrogen screen was used to determine the oestrogenic activity in the extracts. 17β-estradiol (E2) was used as a positive control and the results were expressed as estradiol equivalents (EEq). The EEq of the water from both the communities ranged between 0.63 - 2.48 x10-9 g/ℓ. These concentrations are similar to other studies conducted in Korean river waters in rural and city areas and Flemish surface waters. The recombinant yeast screen confirmed oestrogenic activity in the drinking water samples; further investigation is necessary to determine the source of the contamination and association with impaired growth. <![CDATA[<b>Determining water management training needs through stakeholder consultation</b>: <b>building users' capacity to manage their water demand</b>]]> South Africa is a water-stressed country and the efficient management of the demand for and frugal use of water is a topic that can no longer be avoided. Community-based natural resource management is an alternative approach to government stewardship of natural resources, and in the instance of water management it is a particularly relevant and logical avenue to consider. The Constitution of the Republic of South Africa enshrines the right of the citizens of the country to a healthy environment and to a supply of safe water. These rights are attained through relevant legislation and government action. In this study, the residents of two rural villages in the Steelpoort River basin, South Africa, were interviewed and observed in relation to their water consumption needs and water use practices. The analysis of the research findings resulted in the design of a framework to guide the development of community-based educational programmes related to the management of water demand and water conservation in the Mangabane and Makgemeng communities in the Steelpoort River basin. <![CDATA[<b>Application of the contingent valuation method to estimate a recreational value for the freshwater inflows into the Kowie and the Kromme Estuaries</b>]]> This paper assesses the amount recreational users are willing to pay to secure an increase in freshwater inflows into 2 South African estuaries, the Kowie and the Kromme. A questionnaire was administered to 150 respondents at each estuary site during the period December 2002 to January 2003. The values of freshwater inflows into the Kowie and the Kromme Estuaries were calculated at R0.072/m³ and R0.013/m³, respectively. Total WTP values were estimated at R938 296.59 and R974 019.20, respectively. A valuation function to predict willingness-to-pay was predicted using the Tobit model estimation of linear bid functions. Annual levies paid (consisting of fishing licences, boat registration fees, etc.), distance of current accommodation to estuary, number of household members, primary use of estuary (i.e. recreation or commercial), how informed the respondent was and investment in boats and vehicles were shown to be important predictors of willingness-to-pay in the case of the Kromme Estuary. Level of education, race of respondent, annual levies paid, investment in estuary access equipment and respondent status (i.e., visitor vs. non-visitor) were shown to be important predictors of willingness-to-pay in the case of the Kowie Estuary. An expectations validity assessment indicated that the estimates were credible. <![CDATA[<b>Hydrology, sediment transport dynamics and geomorphology of a variable flow river</b>: <b>the Mfolozi River, South Africa</b>]]> The co-efficient of variation for inter-annual streamflow of the Mfolozi River is extremely high at 79%. An analysis of flow frequency indicated that streamflow is skewed towards low-flow values, with a number of extremely large flood events occurring as outliers on the histogram. Streamflow variability in the Mfolozi River may be linked to multiple factors including a large catchment size, a seasonal climate of a dry winter and wet summer, evergreen vegetation in the catchment, variable precipitation and the occurrence of regionally pervasive climatic oscillations. This research aimed to address how streamflow variability impacted upon sediment transport and thus, geomorphology. It was found that sediment transport variability occurred at the intra- and inter-annual scale. Analysis of mean monthly sediment concentration and discharge showed a hysteresis effect, such that sediment concentration peaked prior to discharge in the early wet season. During the late wet season, peak discharges often had unexpectedly low sediment concentrations. Furthermore, data suggested the existence of long-term hysteresis that may be related to decadal-scale climatic oscillations that alter sediment availability and stream capacity, resulting in discharge peaking in 2000 and sediment concentration in 2005. However, more data are required to confirm this relationship. Variability in streamflow appears to share a causal relationship with sediment transport variability, as both are linked to variation in precipitation and the resultant impacts on vegetation growth and evapotranspiration rates. The variability of streamflow and sediment transport has implications for stream and floodplain geomorphology, and the hydrology of variable rivers should be considered when interpreting their geomorphology. <![CDATA[<b>Sequential injection spectrophotometric determination of V(V) in environmental polluted waters</b>]]> A fast and robust sequential injection analysis (SIA) methodology for routine determination of V(V) in environmental polluted waters is presented. The determination was based on the oxidation of dopamine (DP) by V(V) in acidic medium followed by coupling of the formed intermediary with 4-aminoantipyrine (4AAP) to yield a violet product (λ=565 nm). The operation mode of the SIA system allowed the implementation of a stopped flow procedure in which the reaction zone was stopped for 180 s in the reaction coil before reaching the spectrophotometric detector, with the aim of increasing the sensitivity. Linear calibration plots were obtained for V(V) concentrations between 0.50 and 5.0 mg·ℓ-1. The developed methodology exhibits a good precision, with relative standard deviation (rsd) < 2.0% (n=15) and the detection limit was 0.39 mg·ℓ-1. The presented SIA methodology was applied to the determination of V(V) in 10 water samples and in a wastewater reference certified sample. The determination of V(V) by the developed automatic procedure involved the consumption of 1.9 mg of 4AAP and 2.9 mg of DP and the production of 2.35 mℓ of effluent. <![CDATA[<b>Investigation into the metal contamination of the Plankenburg and Diep Rivers, Western Cape, South Africa</b>]]> Metal contamination in the Plankenburg and Diep Rivers (Western Cape) was investigated over a 12 and 9 month period, respectively. Aluminium (Al), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) concentrations were determined using the nitric acid digestion method and analysed by inductively coupled plasma atomic emission spectrometry (ICP-AES). For both rivers the Al and Fe concentrations were higher than that for all the other metals analysed for in sediment and water samples. The highest concentrations recorded in the Plankenburg River were 13.6 mg·ℓ-1 (water - Week 18, Site B) and 15 018 mg·kg-1 (sediment - Week 1, Site C) for Al, and 48 mg·ℓ-1 (water - Week 43, Site A) and 14 363.8 mg·kg-1 (sediment - Week 1, Site A) for Fe. The highest concentrations recorded in the Diep River were 4 mg·ℓ-1 (water - Week 1, Site A) and 19 179 mg·kg-1 (sediment - Week 1, Site C) for Al, and 513 mg·ℓ-1 (water - Week 27, Site A) and 106 379.5 mg·kg-1 (sediment - Week 9, Site C) for Fe. For most of the metals analysed the concentrations were higher than the recommended water quality guidelines as stipulated by the Department of Water Affairs and Forestry, the Canadian Council for the Ministers of the Environment and the accepted 'world average'. Point sources of pollution could not be conclusively identified, but runoff from both industrial and residential areas could have contributed to the increased concentrations. Metal concentrations should be routinely monitored and the guidelines should be updated and revised based on the current state of the rivers and pollution sources. <![CDATA[<b><i>Acidithiobacillus caldus, Leptospirillum </i></b><b>spp.<i>, Ferroplasma </i>spp.<i> and Sulphobacillus </i>spp. mixed strains for use in cobalt and copper removal from water</b>]]> Bacteria from the genus Acidithiobacillus, Leptospirillum and Ferroplasma, Sulphobacillus are often associated with water remediation. In this study a consortium of Acidithiobacillus caldus, Leptospirillum spp., Ferroplasma spp. and Sulphobacillus spp. was cultured and used to remove Cu2+ and Co2+ from synthetic aqueous sulphate solutions. The influence of experimental conditions such as pH, temperature, time, volume and metal concentration on the efficiency of the biosorption process was investigated. Biosorption of 54 to 67% Cu (pH 2, 37°C, 24 h) and 23-70% Co (pH 2, 37°C, 24 h) was observed from solutions containing 3.86 g·ℓ-1 Cu2+ ions and 3.36 g·ℓ-1 Co2+ ions. Such findings suggest that if optimal conditions for biosorption of the metals by micro-organisms are achieved, this should afford a cost-effective method of removing metal species from water and aqueous solutions. <![CDATA[<b>Removal of copper and cobalt from aqueous solutions using natural clinoptilolite</b>]]> Southern African clinoptilolite capability as an ion-exchanger with respect to Cu2+ and Co2+ was investigated in order to consider its possible application at removing metals from aqueous solutions. The column method was used in the cation-exchange processes with synthetic solution concentrations of 0.07 M (3.86 g/ℓ), 0.33 M (19.31 g/ℓ) and 0.66 M (38.63 g/ℓ) of Cu2+ solution and 0.07 M (3.34 g/ℓ), 0.33 M (16.69 g/ℓ) and 0.66 M (33.37 g/ℓ) of Co2+ solution. Synthetic non-mixed sulphate solutions of copper and cobalt recorded maximum cation uptakes of 79% and 63% with 0.02 M HCl-activated clinoptilolite respectively. From the Cu/Co mixed solutions, both cobalt and copper recorded a 79% uptake with 0.02 M HCl-activation. The 0.04 M HCl activation gave percentage removals of 79% and 77% for Co2+ and Cu2+ respectively. In the ion-exchange evaluation part of the study, it was found that in every concentration range, the adsorption mass ratio of clinoptilolite to metal concentration conformed to both Langmuir and Freundlich adsorption isotherms. However, the non-mixed aqueous solutions of Cu2+ and Co2+ fitted mainly the Langmuir equation. It was found that the adsorption process depends on the hydrated radius of the cation being exchanged, the concentration of the acid that activates the clinoptilolite and the concentration of the targeted cation in solution. <![CDATA[<b>Seasonal study on <i>Bothriocephalus</i> as indicator of metal pollution in yellowfish, South Africa</b>]]> Eighty largemouth yellowfish, Labeobarbus kimberleyensis, were collected between April 2005 and February 2006 with gill nets close to the island (26° 52, 249′ S, 28° 10, 249′ E) in the Vaal Dam. The fish were killed, weighed and their length determined. Muscle, liver and spinal cord tissues were collected from each fish and the intestines removed and opened to expose Bothriocephalus acheilognathi. The tapeworms were collected in glass bottles and frozen. Water and sediment, as well as liver, muscle and tapeworm samples were digested and thereafter metal concentrations of 23 elements (lithium, beryllium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, arsenic, selenium, molybdenum, cadmium, tin, antimony, tellurium, barium, mercury, thallium, lead and uranium) were determined with an ICP-MS. Bioconcentration of metals (selenium, mercury, and lead during autumn; copper, zinc, selenium, cadmium, antimony, thallium and mercury during winter; lithium, zinc, selenium, cadmium and antimony during spring; and zinc during summer) occurred in tapeworms. The highest mean value was recorded in sediment, followed by water, tapeworms and host tissue. A seasonal trend showed that a higher concentration of the metals had accumulated in tapeworms during winter when water levels were at their lowest. <![CDATA[<b>Performance of tubular reverse osmosis for the desalination/concentration of a municipal solid waste leachate</b>]]> Municipal solid waste leachate (MSWL) has the potential to pollute the water environment and to affect biological treatment processes adversely if not properly handled. Reverse osmosis (RO) has the ability to remove both organics and inorganics effectively from effluents. Therefore, RO was evaluated for the treatment of MSWL. It was found that both cellulose acetate and polyamide RO membranes should function effectively for the treatment of the leachate and that it should be possible to control membrane fouling with chemical cleaning. The polyamide membranes, however, performed somewhat better than the cellulose acetate membranes for the treatment of the leachate. The quality of the treated leachate with the exception of ammonia-nitrogen and COD should comply with the quality requirements for discharge into the water environment. Biological treatment processes are effective in complete removal (to only traceable levels) of ammonia-nitrogen and biodegradable COD. The quality of the treated effluent further complies with the quality requirements (chloride and heavy metals) for discharge into the municipal biological treatment system. The capital and operational cost of a 250 m³/d tubular reverse osmosis (TRO) plant is estimated at R1.95 m. and R11.45/m³, respectively. <![CDATA[<b>Practical application and statistical analysis of titrimetric monitoring of water and sludge samples</b>]]> Titrimetry offers the possibility of simultaneous measurement at low cost of several (buffering) components. A first step in the study towards practical application of the titrimetric technique was the titrimetric analysis by up- or down-titration of standard solutions, standard mixtures, solids digester samples and water samples coming from autotrophic nitrogen-removal reactors. The resulting raw data were further processed with an Excel-based program. This program first converts the raw data into a buffer curve upon which a linear buffer capacity model is fitted to the experimental data by estimating the (buffer) concentrations and corresponding pKa values. As such the type of component and the concentration can be determined. As a second step the resulting calculated concentrations were analysed statistically to assess the accuracy and precision of the titrimetric technique. For this purpose, the data were paired, i.e. the difference between the concentration obtained with titrimetry and the concentration obtained with another technique such as colorimetry or gas chromatography was calculated. First the normality of the paired data was assessed. Then, a paired t-test (normal data) or a paired Wilcoxon test (normal data) was used to statistically compare the results obtained with the titrimetric technique to either the stock solution concentration or measurements with another method (colorimetry or gas chromatography). The statistical tests showed that, depending on the titrant concentration, concentrations from 50 mg/ℓ to 3 000 mg/ℓ could adequately be measured with the titrimetric technique. <![CDATA[<b>Treatment of swine wastewater with subsurface-flow constructed wetlands in Yucatán, Mexico</b>: <b>influence of plant species and contact time</b>]]> This study evaluates the capability of horizontal subsurface-flow constructed wetlands (SSF CWs) for treating pretreated swine wastewater as a function of contact time (CT) and type of macrophyte under the local conditions of Yucatán, Mexico. Experiments were conducted from July 2004 to November 2005 on a swine-fattening farm. The study had three stages: first, macrophytes were located and collected; second, plants were acclimatised; and third, a pilot plant with 6 wetlands was set up, operated and evaluated. The effectiveness of the wetlands was intensively tested over 2 periods (April and November 2005). The results indicate that treatment efficiency significantly improved with increased CT for most of the analysed contaminants. The highest removal rates were recorded at a CT of 3 d and ranged between 64 and 78% for total suspended solids, 52 and 78% for COD, 57 and 74% for BOD5, 57 and 79% for total nitrogen, 63 and 75% for ammonium nitrogen, 70 and 81% for nitrate, 0 and 28% for total phosphorus and 3.3 and 4.2 log-units for total coliforms. Results also suggest that the macrophyte species used did not significantly differ on their contribution to overall treatment efficiency. However, vegetated beds slightly improved water quality when compared to unplanted systems. Horizontal SSF CWs are a suitable technology for treating swine wastewater under the local conditions of Yucatán. Contact time should be given special attention in the design of future full-scale facilities. <![CDATA[<b>Low prevalence of antibiotic-resistant gram-negative bacteria isolated from rural south-western Ugandan groundwater</b>]]> The objective of this study was to determine antibiotic resistance patterns and specific resistance genes in Gram-negative enteric bacteria recovered from 42 different drinking water sources servicing 2 rural villages in south-western Uganda. These water sites were prone to contamination by both human and cattle activity. Of the 52 isolates examined, 26 carried antibiotic resistance genes with 25 being ampicillin resistant, 21 carrying the blaTEM gene, and no isolate carrying genes coding for extended-spectrum β−lactamases. Twelve isolates were tetracycline resistant and these bacteria carried between 1 and 3 different tet genes, with the tet(A) gene the most common. Six isolates carried the macrolide resistance mef(A) and/or the macrolide-lincosamide-streptogramin B resistance erm(B) genes. Four isolates carried the sul1 gene, and 4 isolates carried the sul1 and int1 genes indicating the presence of Class 1 integrons. The Ugandan isolates in this study had lower than expected carriage rates of antibiotic and multi-drug resistance genes, carriage of Class 1 integrons and lacked genes coding for extended-spectrum β−lactamases as compared to antibiotic resistance carriage in clinical African isolates. <![CDATA[<b>Two new methods for the determination of hydraulic fracture apertures in fractured-rock aquifers</b>]]> Fracture apertures play a significant role in groundwater systems. For proper groundwater quantity and contamination management, fractures have to be properly characterised. However, due to their complexity, fracture characterisation is one of the main challenges for hydrogeologists all over the world. This is particularly important in South Africa, where aquifers are predominantly fractured. Two new methods have been developed to determine inclined and horizontal fracture apertures in fractured-rock aquifers. The first is a water-balance method, the slug-tracer (ST) test: • The slug-tracer (ST) test [b = (r² / R²) Δ h] and the second is a tracer-detection method, comprising the NAPL entry pressure (NEP) test and the NAPL injection pressure (NIP) test: • The NAPL entry pressure (NEP) test [b = 1/2Pe (r ρ g h)] • The NAPL injection pressure (NIP) test [b = 1/2Pe (ρ g V/ 2 π r)] and [b = 1/4Pe (M g) / m] These mathematical formulations were developed from laboratory experimentation using transparent Perspex parallel plate physical models and 27 apertures of 0.008 mm to 6 mm, created by using aluminium foil and thickness gauges between 20 mm thick clamped Perspex plates. The ST test uses a slug to which is added NaCl as tracer (50 mg to 300 mg/ℓ). An EC meter is used to detect breakthrough in the observation boreholes. The NEP test uses an NAPL (sunflower oil) hydraulic head and transducers to determine the entry pressure. Using these mathematical formulae, fracture apertures are then determined for horizontal and inclined apertures. The NIP test uses the entry pressure (by injection), recorded by transducers of an NAPL (sunflower oil) and its volume or mass to determine the fracture aperture for horizontal and inclined fractures. Results from smooth and rough (buffed to 10 x 20 µ) fracture surfaces gave accuracies of 96 to 98% for aperture determinations of 26 apertures from 0.04 to 6 mm.